Not Applicable
1. Field of the Invention
This invention pertains generally to infrared sources, and more particularly to an ultra-compact, room temperature, continuous-wave, rapidly tunable infrared source.
2. Description of the Background Art
Tunable sources in the infrared spectral region are important for a number of applications, including remote sensing of trace gases. Compact infrared sources operating at room temperature are especially attractive for demanding Department of Defense (DoD) operations requiring high mobility and reliability on both ground-based and aircraft platforms. In many cases, the infrared sources must be able to rapidly tune over a wide spectral range to achieve high-speed measurements on many trace gases.
Although recent research on Quantum Cascade lasers, Type-II lasers, and Solid-state Optical Parametric Oscillators (OPO) have demonstrated impressive results, none of those infrared sources currently offer the desired characteristics listed above. Both Quantum Cascade lasers and Type-II lasers show high power continuous wave operations at cryogenic temperatures; however, their performance degrades at higher temperatures and, further, they cease to operate continuous-wave (CW) at room temperature. Their tunability is also limited by narrow spectral widths, and only relatively slow thermal tuning have been demonstrated. Solid-state OPOs, on the other hand, perform very well at room temperature; however, they require sophisticated bulk-optics alignment between the diode pump laser, the solid-state laser, and the OPO resonator. In addition, their line widths tend to be too broad to resolve dense trace gas lines, and they cease to operate unless the pump power levels are maintained above the threshold in the multiple watt levels.
Accordingly, there is a need for a continuous-wave infrared source that is ultra-compact, rapidly tunable, and operable at room temperature. The present invention satisfies those needs, as well as others, and overcomes deficiencies inherent in conventional infrared sources.
The present invention comprises an ultra-compact, room-temperature, continuous-wave infrared source that can rapidly tune over a very wide spectral range. More particularly, the invention comprises a monolithically integrated device which requires no external pump lasers or bulk optics for its operation. Accordingly, an aspect of the invention is difference-frequency-generation in a highly nonlinear optical semiconductor waveguide with which high power semiconductor lasers can be integrated to internally provide the tunable pump and signal waves.
By way of example, and not of limitation, the invention can achieve a wide tuning range covering one or multiples of the following approximate infrared ranges: 3 xcexcm to 4 xcexcm, 4 xcexcm to 6 xcexcm, 6 xcexcm to 8 xcexcm, and 8 xcexcm to 12 xcexcm. The spectral width of the infrared idler is approximately 10 MHz. The invention employs zinc-blende semiconductors such as GaAs and InP which are excellent nonlinear optical materials as well as superb laser materials. They offer high nonlinear optical susceptibilities (e.g. "khgr"(2)GaAs=180 pm/V), wide transparency in the infrared (approximately 0.9 xcexcm to approximately 14 xcexcm for GaAs), high damage threshold (approximately 10 MW/cm2, inside the facet), and single mode lasing at power levels above approximately 1.0 W. For efficient nonlinear optical processes, advanced material processes, including wafer-scale bonding and atomic-scale planarization, are employed to realize a semiconductor waveguide with patterned crystal orientation for quasi-phasematched interactions. Further, the invention exhibits idler tuning over a wide spectral range by tuning the two laser emission wavelengths.
An object of the invention is to realize an infrared source operating at room temperature and capable of rapidly tuning over a wide wavelength range in an extremely compact and robust device structure.
Another object of the invention is to provide a device that will operate at room temperature, tune over wide infrared wavelengths, and be housed in a self-contained compact package.
Another object of the invention is to provide a compact integrated nonlinear device that achieves room temperature CW operation.
Another object of the invention is to provide a compact integrated nonlinear go device that achieves tunable infrared emission covering the following approximate wavelength ranges: 3 xcexcm to 4 xcexcm, 4 xcexcm to 6 xcexcm, 6 xcexcm to 8 xcexcm, and 8 xcexcm to 11 xcexcm.
Another object of the invention is to provide a compact integrated nonlinear device that achieves a rapid tuning speed of several nanoseconds for tuning from one desired wavelength to another.
Another object of the invention is to provide a compact integrated nonlinear device in a compact device module of approximately 1 cm in length, which contains tunable pump and signal lasers, a MMI coupler, and a nonlinear waveguide.
Another object of the invention is to provide a compact integrated nonlinear device for approximately 3 xcexcm to approximately 4 xcexcm on wavelengths that achieves an approximate 100 mW infrared output if approximately 1 W pump and approximately 1 W signal waves are coupled into the waveguide with a loss coefficient of approximately 2 dB/cm at every wavelength.
Another object of the invention is to provide a compact integrated nonlinear device for approximately 8 xcexcm to approximately 11 xcexcm wavelengths that achieves an approximate 26 mW infrared output if approximate 1 W pump and approximate 1 W signal waves are coupled into the waveguide with a loss coefficient of approximately 2 dB/cm at every wavelength.
Another object of the invention is to provide a room-temperature, continuous-wave tunable infrared source that can rapidly (e.g., less than approximately 10 nanoseconds) tune over a very wide spectral range (greater than approximately 25% of the center wavelength).
Another object of the invention is to provide a continuous-wave tunable infrared source having approximate spectral coverage ranges from 3 xcexcm to 4 xcexcm, 4 xcexcm to 6 xcexcm, 6 xcexcm xcexcm to 8 xcexcm, and 8 xcexcm to 12 xcexcm.
Another object of the invention is to provide a continuous-wave tunable infrared source wherein the spectral width of the infrared idler is approximately 10 MHz.
Another object of the invention is to provide a monolithically integrated infrared source which requires no external pump lasers or bulk optics for its operation.
Another object of the invention is to provide for difference-frequency-generation in a highly nonlinear optical semiconductor waveguide with which high power semiconductor lasers are integrated to internally provide the tunable pump and signal waves.
Another object of the invention is to provide a highly nonlinear optical semiconductor waveguide with which high power semiconductor lasers are integrated to internally provide the tunable pump and signal waves based on difference-frequency-generation.
Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.